1. Field of the Invention
This invention is related to an injector for injection of fluids into a mixing or combustion chamber utilizing combined convective (impinging) and turbulent shear processes for mixing with the ability to have a transpiration cooled face plate.
2. Description of the Related Art
It is known in the art to use injectors for combustion of reactant fluids. The injectors direct the two fluids into the combustion chamber in a controlled manner to achieve a desired release of energy. The three most functional concerns for designing a rocket injector are:
1) hardware heat transfer; PA1 2) combustion performance; and PA1 3) combustion stability.
The performance of the rocket injectors is typically dictated by the propellant mixing and, for a liquid propellant engine, the propellant vaporization. The vaporization process in turn is a strong function of liquid atomization. Both the mixing and atomization of propellants are controlled by the design of the injector.
While impinging jet design in the prior art has resulted in adequate atomization and mixing of the propellants, overheating in the combustion chamber and injector is an ongoing concern, especially for a high performing injector. The overheating may be caused by hot gas recirculation over the injector plate and improper mixing or mixture ratio of the propellants in the wall region. A top choice for impinging jet injector design is unlike jet impingement because of its rapid and efficient mixing process. The problem is its tendency for combustion instability.
It is also known that the injectors are coaxial, such as disclosed in U.S. Pat. No. 5,771,576 to Farhang et al. entitled "Convective and Shear Mixing Injector Assembly " and U.S. Pat. No. 5,660,039 to Sion et al. entitled "Injection System and an Associated Tricoaxial Element", both of which are incorporated herein in their entireties. The injectors may be designed to induce swirling in either fluid. A coaxial design without induced swirling, a shear coaxial injector, improves the over heating problem by having the outer coaxial propellant completely shrouding the central coaxial propellant. The shear coaxial injector also avoids the combustion instability by having a more gradual mixing and combustion process. A downside to the shear coaxial injector design in the slow mixing process that solely relies on the interface shearing effect. Further, the so-called reactive stream separation phenomenon may occur, resulting in poor mixing efficiency. Coaxial injectors with swirl flow design have improved mixing of the propellants, but introduce the risk of overheating of face and wall. Another limitation of the injectors of the prior art is the absence of an inter-element mixing effect, resulting in lower mixing efficiency.
The prior art injectors have been of the convective (impinging) type and/or of the turbulent shear mixing type. Both have advantages and disadvantages. The advantages for convective type injectors (conventional impinging type) include high mixing efficiency, ease of controlling the mixing process by pattern and orientation and lower cost. The disadvantages for convective type injector are high injector and near injector chamber heat flux, possibility of chamber wall oxygen compatibility issues (streaking), difficulty with injector spacing and packaging. It also becomes very difficult and complex to provide transpiration cooling for the face plate near the oxidizer injection for impinging type injectors. The advantages of conventional turbulent shear mixing type injectors (like coaxial) are good flame holding and lower injector and near injector chamber wall heating. The disadvantages for turbulent shear mixing type are lower mixing rate, higher injector pressure drop, less controllability in mixing rate, difficult to cool area near the oxidizer tube tip, limited number of parameters for design and possibility of oxidizer tube vibration and wandering without complex face nut design.
Referring now to Prior Art Figure 1a, a prior art injector 100a for a conventional impinging type injector system comprises a solid face plate 1a through which extends fuel passages 2a and oxidizer passages 3a. The fuel passages 2a extend between a fuel manifold 12a and a combustion chamber 50a. The fuel manifold 12a is depicted above the solid face plate 1a and the combustion chamber 50a is depicted below the sold face plate. The shown oxidizer passage 3a extends between an oxidizer manifold 13a and the combustion chamber 50a, with the oxidizer manifold depicted above the solid face plate 1a and extending between the fuel manifolds 12a.
The oxidizer passage 3a extends through the solid face plate 1a to direct a oxidizer flow 102a perpendicularly into the combustion chamber 50a. The fuel passages 2a are at an angle through solid face plate 1a and are arranged to direct fuel flows 104a to impinge upon the respective oxidizer flow 102a. Other prior art designs of coaxial and shower head injectors direct perpendicularly the fuel flow 104a into the combustion chamber 50a.
A disadvantage of the prior art injector design 100a is the high temperature incurred in the combustion chamber 50a at the solid face plate 1a. Transpiration cooling has been used in non-analogous applications to prevent part overheating. In the prior art for impinging injectors, transpiration of the fuel through the solid-face plate 1a is not directly feasible. Further, if the faceplate was porous or if transpiration holes were manufactured into the solid face plate 1a, the fuel manifold 12a is only in contact with a portion of the face plate, resulting in uneven transpiration and hot spots on the face plate, since oxidizer is not suitable for transpiration cooling of injectors.
As the prior art does not disclose a suitable cooling solutions, i.e. transpiration cooling through the face plate, the use of fuels and oxidizers of elevated temperatures is also not disclosed in direct nor analogous prior art. It is known in non-analogous prior art situations to precombust fuel and oxidizer for other purposes, such as providing rotational power to an upstream turbine, prior to complete combustion of the fluids. However, limitations in the ability to withstand elevated temperatures in the combustion chamber has restricted the prior art in the field of impinging injector design to lower temperature, non-precombusted propellant fluids.